With the right keyboard, you wouldn't even have to worry about being able to sing or play well. You could have the keyboard play a pre-arranged score, and also use it to correct the pitch your voice, while singing into a built-in microphone.
I don't very many people would actually want to do this though, because it isn't very tr00. If you seriously plan to have power metal vocals though, then vocal training is probably the only reliable method of learning how to sing.
As far as learning to play keyboard, I wouldn't worry too much about it. Most metal keyboards are fairly easy, especially in comparison to classical piano or ragtime. You first intuition is that it's going to be hard simply because of how fast it is, but you can built up your speed in no time.
I dont think dragonforce is really hard at all to play, particularly if you are principally a pianist as the keys are so light on a nonweighted keyboard, its easy to whizz around.
just practise your scales, and gradually increase the speed.
Sonata arctica solos are harder as there not so random and have different rhythms.
Are you serious? My keyboard is non-weighted, and I think it's easier and more comfortable to play a piano with weighted keys.
Off Topic...
seeing as you're all keyboardists...
Do you all learn your songs by ear or get tabs/music/MIDI from some unbeknownst source?
I've gone through pretty well everything at SymphonyX.com and Dreamtheater.net
There are a lot of reliable tabs for both Guitar Pro and for TabIt. Either or these programs can be used to export MIDI, so that you can read the sheet music via notation software such as Finale or Sibellius. Alternatively, you can do what I did, and buy a keyboard with lit keys, play your MIDIs through the keyboard, and follow the lights.
